Honors Theses (Environmental Studies Program)

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Browsing Honors Theses (Environmental Studies Program) by Author "Banks, Anna"

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    BAYESIAN BIOGEOGRAPHIC ANALYSIS OF SQUIRREL EVOLUTION SUGGESTS AN ASIAN ORIGIN
    (University of Oregon, 2021-06) Banks, Anna
    Squirrels have an incredibly diverse lineage with a global distribution and have dispersed over millions of years from a common ancestor approximately 40-50 MYA. The assumption since the 1980’s has been that squirrels originated in North America and evolved from North American tree squirrels about 34-39 MYA, but in a more recent study, the oldest giant flying squirrel fossil was found in Oregon suggesting a possible eastward migration from Asia. This study made me question the previously accepted hypothesis that squirrels originated in North America and led to an exploration of squirrel evolution and origins. We used an R package called BiogeoBEARS with Bayesian biogeographic analysis and a DEC+J model to get a better picture of where squirrels were located at different points in their evolution. To run this analysis, we input a phylogenetic tree file, representing 225 modern Sciuridae species, and a biogeography file with each of their locations sorted into eight regions. My analysis resulted in a few noteworthy findings regarding major biogeography changes and their timing: (1) we believe that squirrels originated in Asia, (2) North American and Southern African squirrels came from Asia, and (3) we found one long South American branch, genetically distant from all other South American Sciuridae species and stemming from near the oldest common squirrel ancestor, leading to just one species, Sciurillus pusillus, a modern species that has resided in South America for about 37 Ma.